FIELD OF THE INVENTION
The invention relates to an electronic data processing circuit having an operating module such as, for example, a microprocessor, at least one data memory and a data bus extending between the data memory and the operating module.
Electronic data processing circuits of the generic type are frequently used in applications which are critical with regard to security. In such a case, confidential data, money values and access authorizations which are processed by the operating module, for example upon an external request, are stored in the data memory.
Since the memory contains information which is not to be accessed as far as possible, it is necessary to take security measures against manipulations of the electronic data processing circuit.
When an electronic data processing circuit of the generic type is constructed as an integrated circuit, it can be covered with different passivation layers. In that case, the passivation layers can be applied in such a way that removing a passivation layer entails the destruction of the data memory. Furthermore, the data memory can be buried in deeper lying layers of the integrated circuit, thus rendering access to it more difficult.
A further possibility for protecting an electronic data processing circuit against undesired manipulations is using sensors which sample operating conditions of the electronic data processing circuit. As soon as a value sampled by a sensor is outside a normal value, appropriate security measures are initiated which lead to deactivation of the electronic data processing circuit or else to an erasure of the data memory.
Furthermore, there are also software sensors which monitor the operation of the operating module for forbidden commands or for instances of access to address areas which are blocked for normal operation. Moreover, the access sequence can be monitored for its correctness.
Finally, it is further known for instances of access by the operating module to the data memory which are permitted in a special production mode to be limited by special hardware devices such as, for example, interruptably configured connecting tracks.
Despite the security measures set forth above, undesired manipulations occasionally occur on the electronic data processing circuits of the generic type.